A conventional rotary energy converter of this kind is employed as a hydrostatic hydraulic pump or motor and always uses mechanisms, such as cam mechanisms and linkages, for converting rotary power applied to its input shaft into rectilinear motion of a piston, plunger, or the like and for converting such rectilinear motion of the piston into rotary motion of its output shaft. Since its components are pressed against each other or a twisting force is applied to some components, the converter must employ bearings that make use of either wedging action of oil film utilizing oiliness or viscosity of lubricating oil or rolling action of balls, rollers, or the like. Therefore, an oil having an appropriate viscosity is required to be used as working fluid. If water or other fluid is approximate in viscosity to water is used as working fluid, it will be difficult to operate the converter smoothly. This makes the life of the machine quite short. Thus, working fluids that can be used are limited to certain kinds. If roller bearings are used, the life of the whole machine depends on the life of worn bearings, making it difficult to enhance the durability. Further, roller bearings are relatively bulky. This renders it difficult to make the machine smaller and lightweight.
Recently, an almost ideally efficient flud energy converter which operates on quite different principles from prior art techniques described above has been developed (see Japanese Patent Laid-Open No. 77179/1983). Specifically, this converter comprises a housing having a tapering surface in its inner surface, a torque ring which is closely held against the tapering surface of the housing via first static pressure bearings disposed circumferentially from one another and having flat surfaces corresponding to the first bearings on its inner surface, a plurality of pistons disposed on the inner side of the ring and connected on the front ends thereof to the flat surfaces of the ring via second static pressure bearings, respectively, a cylinder barrel for supporting the bottom ends of the pistons so as to be slidable therein, a pintle which is disposed in an eccentric relation from the axis of the housing and supporting the barrel, spaces formed between each piston and the barrel and which increase or decrease the volume with the relative rotation of the housing and the ring, a pair of fluid communication passages for communicating the spaces whose volumes are increasing and decreasing, respectively, and fluid passages for introducing fluid from the spaces into the first and second bearings. Consequently, the static pressures of the fluid introduced into the first and second bearings develop several forces about the axis of rotation of the torque ring.
In each first static pressure bearing having a single pressure pocket, the center of pressure of each bearing is maintained at a certain position and so other forces, that are produced about a position not lying on the axis of rotation, acts on the ring. This structure is now described by referring to FIGS. 11 and 12, where the static pressure in each first static pressure bearing a produces a force F.sub.a that acts a1ong a 1ine of action L.sub.a. This line L.sub.a passes across the center of pressure (geometrical center) b of the bearing a, and every line of action L.sub.a center on a point d on the axis m of both the housing c and the torque ring k. The static pressure in each second static pressure bearing e produces a force F.sub.b that acts along a line of action L.sub.b. Every such line of action L.sub.b, that is, the center lines g of the pistons f center on a point i on the axis n of the pintle h. Therefore, where the inner surface j of the housing c has a tapering surface if the torque ring k is rotated relative to the housing c by displacing the axis n of the pintle h from the axis m of the housing c, the center g of the pintle f periodically moves away from the pressure center (geometrical center) b of the bearing a while following an elliptic orbit p as shown in FIG. 12. In this case, the movement of the center g relative to the pressure center b along the axis X is needed to produce a couple of forces about the axis of rotation of the ring k. However, displacement along axis Y bends or twists the ring k. This may impair advantageous features of this system, such as excellent durability and the ability to run smoothly and efficiently.